About dinner, what time should I reach the lake in dinner time?Most ryokan serve food between 6 and 8, but some should be able to serve after 8. Please inquire with your ryokan.
Further question, during in Kyoto(7.30am-1.00pm) is it convenient and to visit Kinkakuji, Kiyomisu and Fushimi inari by bus before leaving for Kawaguchiko lake?
Only if you know where to park a bus. Also, you will have to move at a fast pace and check opening hours.